Is the extender like the DirecTV2PC program? Similar as in watching stuff recorded on your DVR on a PC?
No. The Slingplayer software would the analog of DIRECTV2PC. It requires much less of a computer and, because the Slingbox is bandwidth adaptable, can play more readily through a Wi-fi connection.
The Sling Receiver, as it is more properly called, differs from DIRECTV2PC because it supports playback on a television without needing to have an HDCP capable HDTV. The Sling Receiver is also capable of receiving content that hasn't already been recorded as the Slingbox side digitizes in real time. A major difference with the Sling Receiver is that you can actually control the box that it is streaming. You can change channels, look through the guide and set up recordings as if you were watching a conventionally connected television.
Slingbox = sending device
Sling Receiver = receiving device
Slingplayer = receiving software for computers and mobile devices
Slinglink = Homeplug 1.0 Turbo networking adapter.
The recently used designations of Sling Adapter and Sling Extender are exceedingly poor at defining what the devices are used for and I suggest that their use be abandoned.